With the increasing use of small portable electronic devices, the need for small rechargeable battery cells has greatly increased. Single use cells involve a substantial cost to provide the electrical energy for portable units, so that rechargeable cells are used in greatly increasing quantities. There is a problem, however, in the use of such batteries by unskilled persons, in that there is the possibility that the battery can explode while being charged due to excessive pressures which may develop within the battery cell. Similarly, excessive temperatures may be encountered which can damage the battery if some protection is not available.
In connection with rapid charging systems, highly complex arrangements have been used to provide protection for the battery. These systems are quite expensive, have not been very reliable, and are not compatible with conventional cells.
It has been proposed to provide pressure and temperature responsive switches which can be used either inside the battery housing or externally thereof, to disconnect the battery, or to operate some control device to prevent damage to the battery. However, existing structure have required a discrete switch device which involves substantial space in the battery and also involves a cost which substantially increases the cost of the battery. Inasmuch as many portable devices now being produced are quite inexpensive, the provision of a pressure and/or temperature responsive switch in the battery adds a cost item which is quite substantial as compared to the overall cost of the equipment. This may render the device economically unattractive.